Doctor , I slipped and fell on my way to school . The ground is so slippery from the snow . It seems I can't move my left arm now .   Let me see . Roll up your sleeve , please . Um ... it's swollen and red here . I'm afraid we'll need to take an X-ray to see if it's broken .   What if it's broken ?   Then we'll put you in a cast .   What do you mean by a cast ?   Well , we apply tape and plaster to from a solid enclosure to protect the bones from moving . In this way they will heal properly . Take it easy . It won't hurt you . Let me see . The X-ray picture indicates that your humerus is broken in two places . And you'll have to wear the cast for three weeks . You'll need to come back in two weeks , so I can have another look . 